The present invention relates generally to fiber grating type structures, and more particularly to apodized fiber gratings implemented in a chiral fiber structure.
With the proliferation of fiber optic communication lines, the issue of undesirable sidelobes in the spectral response of uniform fiber gratings, resulting in channel crosstalk, has become an important consideration, especially for wave division multiplexing (WDM) applications. The main peak in the reflection spectrum of a uniform chiral fiber grating is accompanied by a series of undesirable sidelobes at adjacent wavelengths. Eliminating these sidelobes by apodizing the reflection spectrum of the grating is crucial in many applications.
A number of solutions to this problem have been proposed over the years. The most successful solution involves the implementation of a nonuniform refractive index modulation at each end of the apodized fiber Bragg grating (FBG) resulting in a sharp spectral response with suppressed sidelobes.
However, the apodized FBG suffers from a number of drawbacks. FBGs are typically fabricated by irradiating a UV sensitive material with UV light through a pre-designed phase mask. The phase mask determines the periodicity and size of the resulting FBG and thus must be carefully designed to provide the desired apodization to an FBG. Because different optical fibers with different lengths and periods require apodized FBGs having different variations of the index of refraction to suppress the sidelobes, a specific phase mask must be designed for each optical fiber line. Finally, due to the fact that apodized FBGs use UV-sensitive materials, the choice for materials is limited.
It would therefore be desirable to provide an advantageous apodized fiber grating that is easy and inexpensive to manufacture and that may be readily customized for any desired application. It would also be desirable to provide an apodized fiber grating that could be made from a broad range of optical materials.